1. Field of the Invention
The present invention relates generally to structural supports for use in refrigerator cabinets employing polyurethane foam insulation and, more particularly, to supports which may be used either generally as stiffening members or as parts of screw-anchoring systems for fastening loads to various panels of the refrigerator cabinets.
2. Description of the Prior Art
In the art of refrigerator cabinet construction, particularly where plastic inner liners are employed, it is frequently necessary to provide selective reinforcement. For example, particular panels in a refrigerator cabinet, which panels may be parts of either the liner or the outer case, may require stiffening. As another example, where shelf supports or the like are attached to the inner liner, particularly a plastic inner liner, some form of support is needed. A mere screw-receiving aperture in the plastic is generally unsatisfactory, except where extremely light loads are involved, because insufficient area for thread engagement results and the entire load is concentrated on a very small portion of the plastic material. This can result in undesirable deformation or even cracking of the plastic sheet.
In a typical refrigerator construction, metallic plates are used generally as stiffening members where needed. In a more specific application, where a load is to be applied to a plastic inner liner, metallic or plastic back plates are employed. One typical specialized device for this last-mentioned purpose is known as a screw anchor and is generally formed of plastic. A screw anchor is applied to a suitable aperture in the liner, generally from the rear side thereof. The screw anchor includes a bore for receiving a screw and, additionally, a relatively large diameter, force distribution portion for contacting a significant area on the rear side of the plastic liner. This, of course, serves to distribute the load over a greater portion of the liner material. Additionally, when insitu foamed polyurethane insulation material is used within the refrigerator wall space, suitable projections on such a plastic screw anchor bond to the foam insulation material so that a portion of the applied load is transmitted to the foam.
Where exceptionally heavy loads must be applied to the inner liner, a separate metallic or molded plastic member may be employed which actually bridges between the inner liner and the outer case to transmit the applied interior load directly to the metal outer case.
There is another prior art construction which would appear to be unrelated to the present invention. However, in view of the nature of the invention, as will hereinafter become more apparent, this prior art construction is worthy of mention. In refrigerator constructions where insitu foamed polyurethane thermal insulation material is employed, during the foaming process, after injection of the foam reactant material but prior to solidification and hardening of the foam, large forces are developed which tend to force foam material through any available cracks or openings. Around the front face of a refrigerator cabinet there is generally an interface between a separate outer case and the inner liner. For example, the outer case may be made of steel and the inner liner of plastic. In order to prevent foam material from leaking through any crack which may be associated with this interface, a "foam stop" seal is typically employed. One foam stop which is typically employed is a suitably shaped, elongated body of glass fiber material applied around the periphery of and behind the front face. During the foaming process, when the polyurethane foam material contacts the foam stop, it penetrates and impregnates the glass fiber material approximately one-fourth inch. The foam material is thereby stopped and prevented from leaking through the crack. Upon solidification of the foam material, at the interface between the foam insulation and the glass fiber stop there is a region of rigid, dense material. This material occurs as a side effect of the foaming and sealing process, and other than being a part of the foam stop, it serves no particular purpose, although some rigidity may be added to the cabinet thereby.
In connection with glass fiber material, it is of course well known to employ such material to reinforce epoxy resin. This results in the hard structural material commonly known as "fiber glass," which is used to form the shells of any number of objects such as boats, automobiles, and storage tanks, where high strength is required. Such fiber glass material is to be distinguished from the material which results when polyurethane foam material impregnates glass fiber material. The latter, although relatively hard, is not nearly so hard as glass fiber reinforced epoxy resin, and it can be partially deformed, particularly by insertion of elongated objects with moderate forces and without the cracking of the body of material. It is also somewhat elastic. The properties of this material formed when polyurethane foam material penetrates the glass fiber material are related to the properties of the polyurethane foam itself, in that a body of polyurethane foam is rigid, yet has elasticity and a slightly "spongy" feel such that it can be moderately deformed without breaking.